Galvanometer relay



April 19, 1938. A. J. MCMASTER ET AL 2,114,853

GALVANOMETER RELAY Filed Sept. 5, 1936 4 Sheets-Sheet l A ril 19, 1938. A. J. MCMASTER ET AL GALVANOMETER RELAY Filed Sept. 5, 1936 4 Sheets-Sheet 2 April 19, 1938. A, J. MCMA'STER ET AL 2,114,853

GALVANO ET'ER RELAY Filed Saint. 5, 1956 4 Sheets-She et a A. J. McMASTER ET AL GALVANOMETER RELAY April 19, 1938.

Filed Sept. 5, 1936 4 Sheets-Sheet4 Patented Apr. 19, 1938 PATENT QFFECE GALVANOMETER RELAY Archie J. McMaster, Highland Park, and Walter Van Guilder, Oak Park, Ill., assignors to G-M Laboratories, Inc., Chicago, 111., a corporation of Illinois Application September 5, 1936, Serial No. 99,672

22 Claims.

The present invention relates generally to electric relays and more particularly to relays which are highly sensitive in that they require only very small amounts of power for controlling them.

The relay of the present invention comprises a taut suspension DArsonval galvanometer movement and a clamping and contact operating mechanism adapted to clamp a pointer carried by the galvanometer coil. The galvanometer movement, in response to the control current in its coil moves its pointer into or out of the position in which it may be engaged by the clamping jaws or bars, and the clamping mechanism periodically attempts to clamp the pointer. Contacts are operated each time that the pointer is caught between the clamping jaws.

The relay of the present invention employs a plurality of independent contacts operated by separate clamping jaws or bars which are disposed at various positions along the arc of travel of the galvanometer pointer. It includes also mechanisms for conveniently moving or adjusting the clamping jaws along the path of travel of the galvanometer pointer so as to vary the values of control current at which the pointer encounters or escapes particular clamping jaws.

- The adjusting mechanism is arranged to prevent any adjustment of the jaws while they are in a clamping attitude with respect to the pointer.

The invention further provides means for indica'ting visually on a graduated scale both the deflection of the galvanometer needle and the adjusted position of the clamping members. The present invention further provides new and novel mechanisms for providing the operations and functions mentioned and described above.

t is an object of the present invention to provide an improved relay of the type indicated, which is rugged and reliable and otherwise suitable for use in industrial control apparatus.

It is a further object of the present invention to provide improved apparatus for performing the above described functions.

Theseand other objects and advantages of the present invention will become apparent as the description proceeds.

The following description of a specific embodiment of the present invention, when taken in connection with the accompanying drawings will enable those skilled in the art readily to understand the invention and to practice the same. In the drawings:

Fig. 1 is a general view in perspective of the (Cl. ZOO-56) exterior of a relay embodying the present invention;

Fig. 2 is a general view in perspective of the internal mechanism of the device illustrated in Fig. 1;

Fig. 3 is an exploded view showing some of the pieces and partial assemblies of the apparatus of Figure 2 individually in perspective;

Figs. 4 and 5 are horizontal and vertical sections respectively of the device of Fig. 1, Fig. 4 being a section taken along the line 44 of Fig. 5, and Fig. 5 being a section taken along the line 5-5 of Fig. 4;

Fig. 6 is an elevation partly in section taken along the line 66 of Fig. 5;

Fig. 7 is a section taken along the line l-'! of Fig. 5;

Fig. 8 is a section taken along the line 8--8 of Fig. 6;

Fig. 9 is a partial view showing the apparatus of Fig. 4 in a diiferent operated position; and,

Fig. 10 is an enlarged sectional detail taken along the line llllil of Fig. 4.

The apparatus illustrated in Fig. 2 includes a DArsonval galvanorneter and a contact making mechanism controlled by the galvanometer. The galvanometer itself comprises a die-casting ID of non-magnetic material such as a zinc alloy. (See Figs. 3, 4 and 5.) The die casing It] serves as a housing as Well as a supporting frame for a portion of the galvanometer apparatus. A pair of iron pole pieces ii and i2 (Fig. 3) are imbedded in the die-casting l and each pole piece extends from the exterior of the casting or housing In entirely through the wall thereof into the interior cavity thereof. Preferably, the pole pieces II and 12 are placed in the mold at the time the die-casting I8 is struck so that the casting is formed about the pole pieces II and !2. The pole pieces conveniently may have irregular surfaces such as identations l4 shown in the section of Fig. 8 into which the metal of the die casting may flow for securely locking the pole pieces in position.

Supported on a boss it of the die-casting I!) (Fig. is a core l5 positioned between the two interior faces of the pole pieces H and I2 so as to provide two air gaps as shown in Figs. 3 and 8. Like the pole pieces H and l2, the core l5 is of iron or similar magnetic material. A magnet 26 (Figs. 2 and 5) completes the magnetic circuit and provides the magnetic flux in the two gaps already mentioned.

A coil IT is supported on two taut suspension wires I8 and 19 which in turn are supported on resilient metal tabs 2| and 22 (Figs. 3 and 5). These tabs 2| and 22 in turn are supported on insulating disks 23 and 24 which are directly supported by the die-casting ill. The loop shaped coil H has one of its sides lying in each of the air gaps provided between the core 55 and the pole pieces H and i2. A pair of nonmagnetic plates 2? and (Figs. 3, 5 and 8) are placed over the core l5 and cover the two magnetic gaps near the tips of the pole pieces and i2 so as to confine and protect the coil i l.

The two suspension wires l8 and I9 consist of very fine gold ribbon or the like, and the-y are held taut by the resilient tabs 2| and 22. The resilient tabs 2| and 22 support these ribbon suspensions |8 and 19 at the center of the disks 23 and 24 so that the axis of rotation of the coil l7 coincides with the centers of the disks 23 and 24. The suspension wires l8 and 53 not only support the coil l'i mechanically but they also serve as the electrical connections thereto, the adjacent ends of the wires l8 and |9 being connected tothe winding of the coil H for this purpose. The torsion of these wires provides the restoring force of the coil. Each of the two insulating disks 23 and 24 is rotatably adjustable in the casting it) for setting and adjusting the rest or Zero position of the coil As best may be seen in Figs. 3 and 7, the upper disk 23 is notched and this notch is adapted to engage an internal projection ill of a rotatable cap 32. This cap 32 fits onto the die-casting II] and rotates thereon about an axis substantially concentric with the center of the disk 23. The projection 3| of the cap is adapted to engage shoulder faces 32 of the casting l so as to limit the angle through which the disk 23 may be rotated. The cap 32 is adapted to be rotated manually by the users of the instrument so as to permit manual rotation of disc 23 for correcting the zero position of the coil IT. The limited angle of rotation prevents the user from carelessly or accidentally rotating the disc 23 continuously in one direction to thereby damage the suspension wire l8 by twisting it excessively. The disk 24 also rotates in the casting Hi. This disk is not provided with any stops for limiting its rotation because it is not accessible for adjustment unless the device is partially dismantled. It is intended to be used only as a factory adjustment.

Secured to the top of the coil ii is a piece of formed non-magnetic wire 35 (see Fig. One end of this wire extends upwards substantially parallel to, alongside and in front of the upper suspension wire l8 and bends forward at a right angle for receiving a pointer 36, which consists of a thin-wall aluminum tube. This tube carries a small fiber bushing 3'3 near the outer end thereof to protect it and prevent it from collapsing under the mechanical force of the clamping mechanism to be described presently. The extreme end of the pointer 36 is collapsed for bending it and also for providing a blade like portion 38 for cooperating with a visual scale 39. (See Figs. 2, 3 and 5). The other end of the wire 35 (see Fig. 5) extends back from the coil IT at right angles to the suspension wire |8, that is, in a direction opposite to that of the pointer 36 and its bushing 31. It extends through an aperture in the main galvanometer die-casting It) and carries at its end a counterweight M for balancing the weight of the pointer 36 and its bushing 31. A box-like cover 42 closes this aperture and gives the counter-weight 4| room to swing from side to side within the enclosure as the coil rotates.

A pair of terminal screws 43 and 44 (Fig. 5) are secured to the casting ID with insulating washers. These terminal screws are connected to the spring tabs 2| and 22 to provide electrical connections to the coil ll of the galvanometer. The wire 45 connecting the terminal 23 to the upper tab 2| extends from the tab 2| down through the hole in the disk 23, then down along the interior wall of the casting l0, passing between the wall of the casting l0 and the guard plate 28 at one side of the boss l6, all to avoid touching the suspension 8, the coil IT, or the wire 35 which carries the counterweight 4 A galvanometer front plate 46 (Figs. 5, 6 and 7) fits over the die-casting Ill so as to close entirely the bottom and front thereof except for an opening at the front near the top where the pointer 36 emerges. The plate 46 includes a tab or tail 4? which hooks under the U portion of the magnet 26 for supporting the weight thereof and for holding the magnet in position on the pole pieces H and I2. The plate 46 also includes lateral projections 48, 49, 50 and 5| which support the magnet at the front. A bar 53 secured to the back of the die-casting I0 supports the magnet at the back and clamps it against the projections 48, 49, 5|] and 5|.

The front plate 46 also supports an electric motor 55 (see Figs. 2 and 5) and a bell crank 57, (see Figs. 3, 5 and 6) which constitute a part of the clamping and contact operating equip ment. The electric motor 55 preferably is of a type which operates on alternating current and employs shading coils for obtaining a magnetic phase displacement which in turn produces the effect of a rotating magnetic field for turning the rotor. The motor includes coils 60, a magnetic field structure 6|, shading coils 62, and an enclosed rotor structure 63. The rotor structure 63 includes a reduction gear (not illustrated in detail). The single shaft 64 extending from the reduction gear turns at a slow speed, such as, for example, a speed of one revolution per minute. The shaft 64 carries a cam 65 which operates the bell crank 5'|. Thus the motor lifts the clamping mechanism through the bell crank 51 once each minute.

Referring particularly to Fig. 2, the clamping mechanism includes a pair of clamp bars H and 32 which are adapted to be raised periodically by the electric motor 55. These clamp bars are arcuate in contour and lie under the path of travel of the bushing 31 on the pointer 36. Above the bushing 31 is an arcuate stationary bar 13 against which the bushing 31 is adapted to be pressed by the bars 1| and 12. The galvanometer structure including the pointer 36 as well as the resilient tabs 2| and 22 which support the taut suspension wires l8 and I9 (see Fig. 5) are sufficiently resilient to permit the pointer 36 to be moved this slight distance to be brought into engagement with the bar 13. Quite obviously, the bushing 31 normally must lie a small distance removed from the upper, or stationary, bar 13 because it can not be permitted to touch the bar 73 at the time that it is required to move under force of the current in the coil IT or under the restoring force of the suspension wires l8 and I9.

The separate clamp bars H and 12 have separate contacts 14 and '55 associated with them which they are adapted to operate. A clamp bar operates its contacts only when it catches the .with the roller 19.

pointer between it and the bar I3 as it is raised by the motor 55. The arcuate clamp bars II and I2 are separated by a slight gap sufficient to receive the bushing 31 and thereby permit the pointer 36 and its bushing 31 simultaneously to escape both bars. The two clamp bars II and I2 are adapted to be rotated about the axis of rotation of the pointer 36 so as to permit the gap between the arcuate clamp portions H and I2 to be set at any position along the path of travel of the bushing 31 carried by the pointer 36. If the pointer occupies a position at either side of this gap at the time the clamp bars TI and 72 are raised by the motor '55, it will be caught by one of the bars so as to cause that clamp bar to operate its contacts.

The construction of the individual parts of the clamping and contact making mechanism may be seen best in the exploded view of Figure 3.

Referring to Figs. 3, 4 and 5, a ring shaped rocker I6 is pivoted, by means of pins which are fastened in the rocker IE, to the die-casting W at IT and I8 where the casting is given extra section for that purpose. These two pins which carry the rocker "I6 lie on an axis which is substantially perpendicular to the axis about which the coil ET rotates and which also is substantially perpendicular to the pointer when the same is in its median position in its limited arc of motion. A pair of arms depending from the rocker 16 at its forward side, and at a position removed from the axis of its support on the casting I0, carry a roller I9 which is engaged by one arm of a bell crank 51.

The bell crank 51 is journaled on the ga1- vanometer front plate 46 at a position to one side of the roller 19 and off the axis of the slow speed shaft 64 of the motor 55. The cam 65 carried by the shaft 64 engages the bell crank 5'! and slowly oscillates it. The crank 51 in turn oscillates the rocker I6 by periodically lifting and lowering its forward side through the engagement The weight of the clamping apparatus carried by the rocker IE (to be described presently) provides a restoring force for maintaining the roller 19 in engagement with the crank 51 and also for maintaining the crank in engagement with the cam 65. If desired. spring may be added to the mechanism for increasing this restoring force.

The rocker I6 includes on its periphery a circular seat for a ring 8I which is adapted to rotate thereon. The center about which the ring SI rotates on the rocker I is substantially coincident with the center of rotation of the coil ii, that is, the position of the suspension wires I8 and I9, when the rocker 16 is in a level position. The ring 8! has teeth 82 (see Figs. 3 and 4) formed in its periphery so as to face approximately upward. These teeth are adapted to engage a screw or worm I I4 located just above it at the rear portion of the ring 3| (see Figs. 4 and 5) so that the ring 8| may be rotated on the rocker iii in a manner to be described more fully presently, and so that the teeth 82 may disengage the worm l 94 in a manner also to be described. The rocker I6 and the ring 8i are notched at their front portions to permit their being put in place on the die casting I0 or removed therefrom While the pointer 36 of the galvanoineter is in place ther by facilitating assembly. A pair of resilient clips I02, one of which is shown in each of the Figs. 3 and 4, are secured to the top of the rocker I6. They engage the upper surface of the ring 8| to hold it in assembled relation with the rocker I6 and frictionally to restrain rotation of the ring 8| on the rocker "IS.

The ring SI carries a pair of clamp frames 83 and 84 which are secured to projections 85 and 85 thereof by means of pins such as pin 81, the frames 33 and 8d being free to swing up and down about these pins through a considerable angle. These frames 80 and 84 include the arcuate clamp bars Ii and I2 already referred to. Extending under the clamp frames 83 and 84 are contact structures which include the contacts 14 and '25 already referred to.

The details of the contact structure may be seen best Fig. 16 which is an enlarged sectional view of the contact structure I4 associated with the clamp frame 83. A portion 89 of the ring extends out below and between the projections 85 and under the clamp frame 83. A sheet of fiber 9i somewhat wider than the portion 89 of the ring 8i is Wrapped about the portion 89 and the contact assembly is attached under it, the parts being added in the following order: Resilient contact blade 92, a terminal piece 93, an insulator 9 1, resilient contact blade 95, terminal piece 526 and a capping plate 91. A capping plate similar to plate 91 is also placed over that portion of the fiber piece 9! which lies above the extension 89 of the ring 8!. A pair of insulating bushings iiii extend through the entire assembly excepting only the two capping plates 97 and 90. A pair of rivets !02 extend through the entire assembly for holding it together. The wide piece of fiber 9! extends beyond the several contact ieces and also beyond the piece 89 of the ring SI for the purpose of providing the large electrical clearances required in industrial apparatus for circuits of commercial voltages such as, for example, 230 volts. The structure just described supports the two resilient contact blades 92 and 95 on the ring 8! and insulates the ring BI and each of the separate contact blades 92 and 95 from each other. The blades 92 and 95 carry contact buttons at their ends which are adapted to engage each other so as to constitute the contaste it already mentioned.

The clamp-frame 33 being pivoted at 81 rests on the contact blade 92 so that its weight is supported thereby. The tension of the blade 92 must be sufficient to support firmly the frame 83; and the spring 02 must be adjusted to bring the arcuate clamp bar ll of the frame 83 slightly below bushing 3'! on the pointer 36 when the entire contact assembly has been dropped to its low position by the motor 55. The blade 95 is adjusted so that its contact is spaced slightly from the con tacts of the blade 92 and so that when the contact assembly is raised by the motor 55 and the bar it engages the bushing 37 on the pointer 36 and presses it against the bar 53, the contacts will be brought into engagement, A similar contact assembly is associated with the clamp frame 84 its arcuate clamp bar 12.

A cover IE5 is secured to side extensions I06 and if of the main die casting IS, the cover I05 being provided with bosses I09 and I I0 for that purpose (Fig. 2). The cover I05 is molded of a condensation product but may be die-cast of metal. The cover 105 has an aperture through which the cap 32 extends, and the cover I05 fits over a rim Hi of the cap 32 to retain it in place atop the main die casting I0. The cover I05 has journaled therein a shaft H3 which carries the Worm H4 engaging the teeth of the ring 8| as already described.

A resilient bowed washer II6 on the shaft H3 at one end of the worm lit holds the shaft H3 in a fixed position axially so as to hold the ring 8| and the clamp bars ll and 72 firmly in any position to which they may be adjusted. The end thrust thus provided between the shaft H3 and its bearings serves frictionally to restrain rotation of the worm ti l so as to maintain its adjustment. The shaft H3 also carries a knob H5 outside of the cover 5235 to permit the shaft and the worm M l to be rotated manually for adjusting the angular position of the ring 3% on the rocker 76 and for thereby adjusting the position of the clamp bars ii and 12 along the path of travel of the pointer 36.

In the position in which the clamping and contact mechanism including the rocker '56, the ring 8! and contact bar '52 is shown in Fig. 5, the bar 12 is in its lowest position so as to avoid engaging the bushing 37 carried by the pointer 36, and the teeth of the ringtii engagethe threads of the worm l M. While the apparatus is in this condition, the shaft H8 and the worm HA may be rotated by means of the knob H5 so as to rotate the ring Si in its seat on the rocker it and thereby to move the gap which occurs between the two clamp bars "H and l2 to a different position along the path of travel of the bushing 3?. Fig. 9 illustrates the clamping and contacting mechanism in a slightly different operated position. In Fig. 9 the clamp bar ll has been raised by the motor 55 to the position in which it just initially touches the bushing 31 carried by the pointer 38. At this position of the rocker l8 and ring 8!, the teeth of the ring 3| have moved down and away from the teeth of the worm Ht so as to clear the same. In this connection it is to be observed that the axis of the pins Ti and it about which the rocker l6 tilts is forward of the worm H4, so that, as the clamp bars H and 12 are raised, the rear portion of the ring 8i drops to carry its teeth out of engagement and clear of the teeth of the worm I M. It is desirable that the teeth of the ring 8| should entirely clear those of the worm i 54 before either clamp bar touches the bushing 3'1 carried by the pointer 36 so as to prevent the clamp bars from being rotated manually when the apparatus is in such a condition that the needle 36 might be carried along with the clamp bars. In any event, these teeth should clear before the bushing 31 has been pressed against the stationary bar 13, since then any motion of the clamp bars would tend to roll the bushing'id between the clamp bar H for example and the stationary bar 753, and rotate the needle on the wire 35.

The cover H35 also carries the scale 39, which may be constructed of transparent cellulose material. The scale 39 includes a curved strip of transparent material having a series of ruled lines and numerical indexes 52E printed thereon to provide the graduations and characters with respect to which the positions of the pointers 3t and I22 are to be read. (Pointer !22 will be described presently.) Preferably the characters I 2! are printed on the inside or back surface and are adapted to be viewed through the transparent material of the scale. The printed strip is then coated on its back or inside surface with an opaque material having a color contrasting with that of the printed characters. The coating is omitted immediately above and below the graduations 21 so as to leave windows H9 and i228.

he pointer has its flat or blade portion 38 directly behind the upper window I20 through which it may be viewed so that its position may be noted visually with respect to the graduations of the scale.

The clamp frame 84 carries the pointer I22 extending from the front face of the arcuate clamp bar 1'2. into alignment with the gap between the arcuate clamp bars ii and 12, and it terminates near the lower window I IQ of the scale 39 through which it may be viewed for reading its position with respect to the scale. The portion of the pointer E22 which is visible through the window of the scale is aligned with (i) the center of rotation of the coil ill and pointer 36 of the galvanometer and (2) the gap between the two arcuate clamp bars 1! and I2. cates that position of the scale at which the pointer i335 will avoid being caught by either of the two arcuate clamp bars H and 12. When the pointer 36 occupies a position to the right, as viewed in Figs. 1 and 2, of the position indicated by the pointer i222, the pointer 36 will encounter the arcuate clamp bar 72 so as to cause an operation of the contacts associated with that clamp bar each time that the clamp bars are raised by the motor 55 acting through the crank' 57, rocker it etc. Similarly, when the pointer occupies a position to the left of the position indicated by the pointer I22 it will be caught by the clamp bar H so as to cause an operation of its contacts 74.

The pointers 36 and I22 must be so arranged as to avoid striking or interfering with each other. This will be discussed presently.

The pointer 36 of the galvanometer is capable of swinging through a limited angle of approxi-- mately For this reason, the graduated portion 526 and the windows l H] and I20 of the scale 39 are limited to the central portion thereof. These graduations and windows extend along the entire path or angular sweep of the pointer 36. Each of the arcuate clamp bars H and 12 is sufiiciently long that it alone can cover the complete range of movement of the pointer 36. Thus, the ring 8! may be rotated in a clockwise direction as viewed in Figure 4 so as to bring the pointer in just beyond the extreme left deflectable position of the pointer 36. With the clamp bars in this condition, the pointer 36 will be caught by the clamp bar '52 each time that it is raised by the motor 55 regardless of the position that the pointer 35 may occupy along its entire path of travel. Similarly, the clamping and contacting mechanism may be adjusted by rotating the ring 85 to bring the pointer I22 just beyond the extreme right deflectable position of the pointer 36 so that the pointer 36 will be caught by the clamp bar ll regardless of the position which the pointer may occupy. Obviously, the mechanism may be adjusted to bring the pointer I22 to any part of the graduated portion [2| of the scale 39. With the pointer I22 set at some position along the graduated scale l2! intermediate the limits of the travel of the pointer 36, the bushing 38 of the pointer 36 will engage either the clamp bar ill or the clamp bar 72 depending upon whether the pointer 36 lies to the left or to the right of the pointer H2 at the time that the motor 55 raises the clamp bars.

The cover 65 is made sufiiciently wide to permit this full scale adjustment of the clamping bars, that is, to permit the pointer Hi2 and the gap between the clamping bars to be set at any position along the graduated scale. Thus, for example, when the pointer 22 is set at the left end of the graduated portion it! of the scale,

This pointer is offset to bring it Therefore, the pointer I22 indithan the thickness of the bushing 31.

and the clamp bar II lies entirely to the left of the left end thereof. The cover I05 extends beyond the graduated portion I2I of the scale to enclose the clamp bars in this position.

The pointer I22 and the blade or tip 38 of the pointer 36 must be so limited in size as to prevent them from interfering with each other. When these two pointers occupy the same position with respect to the graduated scale H8, that is, when the pointer I22 is directly below the pointer 36, the bushing 38 of the pointer 36 is directly aligned with the gap between the two arcuate clamp bars II and I2. Therefore, when the clamp bars are raised by the motor 55, the pointer 36 will slip into this gap so as to escape both clamp bars and it will not be lifted thereby. However, the pointer I22 which is carried by the clamp bar I2 will rise therewith. Inasmuch as the clamp bar I2 does not encounter the pointer 36, that clamp bar will rise to approximately the position in which it touches the bar I3 and the pointer I22 will be carried to a higher position than it would have been carried had the clamp bar I2 caught the pointer 36. Therefore, the pointer 36 and its .tip 38 when in its normal unclamped position must entirely clear the pointer I22 when the latter is raised to its uppermost position by the motor 55.

In the construction shown in the drawings wherein the stationary bar I3 is directly above the moving bars II and I2, the difference in the distance which the clamp bar II, for example, rises when it encounters the bushing 31 on the pointer 36 and when it does not, can be no greater That is, the motion of the clamp bar 'II with respect to the ring 8| on which it is mounted and also with respect to the contacts on which it operates, is no greater than the thickness of the bushing 31. Therefore, in the construction shown in the drawings, wherein the clamp bar operates the contacts directly, the spacing between the contacts 92 and 95, for example, must be less than the thickness of the bushing 31. Alternatively, the lower bars II and 12 may be offset with respect to the upper bar I3 so that when the bars do not engage the pointer, the rising bar is free to move past the stationary bar and rise considerably above it. This arrangement permits the motion executed by the clamp bar in operating the contacts to exceed considerably the thickness of the pointer at the position in which it is clamped (for example at the bushing 31). However, offsetting the bars in this manner imposes a bending moment upon the pointer which can be avoided only by employing an extra bar. Thus, the lower clamp bar may be arranged to rise between a pair of parallel stationary bars. However the clamping surfaces of the two parallel bars must be finished with a high degree of precision in order to insure that the pointer engages them simultaneously. Therefore, where a motion equal to the thickness of a bushing (such as the bushing 31) which can be carried by the pointer is sufficient, it is preferred to have the two clamping bars aligned with each other as shown in the drawings.

The relay of the present invention is not continuously responsive, in that it is not immediately responsive at all times to a change of current in its coil IT. This results from the fact that the position of the pointer is tested only intermittently by the clamping and contacting mechanism. It is incapable of responding reliably to transient eiTec'tsv or other conditions which have a duration less than the period of the periodic motion of the clamping mechanism. The instrument controls the operation of the contacts only in accordance with the position which the pointer occupies at the instant that it is caught by the clamping jaws. Thus, for example, if the clamp bars are in the clamping position, the current in the coil Il may change suddenly by a considerable amount but the coil and pointer can not rotate in response thereto because the pointer 36 will be held mechanically by the clamp bars. When the pointer subsequently is released, it will seek the position corresponding to the new value of current in the coil and when the clamping jaws subsequently are brought together again the relay will respond to the new value of current in the coil. However, if the current in the coil should return to its previous value, and the coil and pointer should respond thereto before the clamping jaws again grip the pointer, the relay never will have responded to that particular current condition because the condition will not have persisted for a long enough period of time. In order to make the present instrument as rapid as possible in operation, it is desirable, under certain circumstances, to test the position of the pointer as frequently as possible. In order to permit the instrument accurately to indicate the value of current in its coil, the period during which the pointer is left unclamped should exceed somewhat the time required by the pointer to move to a new position and come to rest. This time is approximately of the period of vibration of the instrument. It is further desirable to operate the clamping mechanism as rapidly as possible so as to consume as little time as possible for the clamping or testing operation. However, the clamping bars should rise slowly enough to engage the pointer 36 gently so as to avoid imposing excessive stress on the galvanometer movement and also to avoid disturbing the position of the pointer by striking it sharply. Furthermore, the speed with which the clamping mechanism may be brought into a clampingattitude may be limited by the power capacity of the motor 55. Accordingly, the cam 65 is arranged to lift the clamping bars with an even and gentle motion and then to drop them rather rapidly to their lowermost position where they are held stationary for a period of time which is at least as long as the time required for the pointer 35 to assume a new position and to come to rest therein. However, in many applications, such as temperature control applications, the rate at which the condition to be controlled is capable of changing will be so slow that the frequency of operation of the clamping mecha nism may be much less than the maximum of which the instrument is capable.

A plate I25 fastened to bosses I26 and I2I of the cover I55 serves to close the forward portion thereof. The plate I25 serves to protect the contacts and the pointers from accidental damage and also aids in excluding dirt from the interior of the galvanometer, the die casting I0 being open at the position at which the pointer 36 emerges therefrom. The entire relay assembly thus far described may be mounted on an enclosing casting I38, shown in Fig. l, which is adapted for mounting on a vertical panel. The relay is mounted on the casting I30 by means of screws entering tapped holes in bosses I32 of the cover I05 (see Fig. 4). Electrical connections are made to the winding 60 of the motor 55 and to the terminal plates (such as 93 and 96 in Fig. 9) of the contacts 5 and i5 may be carried out of the cavity within the casting H15 where the contacts are located through openings H33 at the extreme sides and rear of the cover its,

4 left uncovered by the plate I25.

Although the contacts M and '55 are shown and described as being of the normally open type, normally closed contacts or other more complex contact arrangements may be provided instead. 10"

with or without gaps between them. Where no gap is provided'between two clamp bars, it is possible that the two adjacent clamp bars may be operated simultaneously.

It is to be observed that the clamp bars H and 12 rise with a gradual motion and that the cam 65 may be so arranged that the clamp bars also drop with a gradual motion. Under such conditions the time during which the contacts controlled by a clamp bar are closed or otherwise in an operated condition will depend upon the motion which the clamping mechanism executes on the upstroke, after the contacts operate, and therefore upon the slack motion or motion which it executes before the contacts operate, the total motion as determined by the cam 65 being fixed. It is desirable under certain conditions that the manner of operating the contacts should depend in part upon the position of the pointer along the clamp bar. By cutting the top of the clamp bar H, for example, ofi at an angle, or by pivoting the clamp bar at an angle as by tilting the pin 37, the clamp bar will be made to hold one portion of its clamping surface higher than another. If the pointer is caught by this high portion, the clamp bar will encounter the pointer sooner and disengage it later so as to hold its contacts closed for a longer period of time than if the pointer is caught by a low portion of the bar. Thus, the two bars H and 72 may be arranged to be low near the gap between them so that the length of time in which the contacts are closed increases with the deviation of the position of the pointer 36 from the position of the pointer 522. Thus, the apparatus which the relay of the present controls may be arranged to ,correction required. Alternatively, the bars H and '12 may be notched or stepped to provide a graduated response of the type indicated.

In the relay of the present invention a considerable advantage accrues from the fact that the clamp bars H and i2 are rotatable about the same axis as the coil H and its pointer 36. This permits the clamp bars to be so arranged as always to engage the pointer at substantially the same portion thereof so that the comparatively heavy bushing 38 need not extend along more than a very small part of the total length of the pointer 36. It also permits the upper or stationary bar 73 and lower bars ll and 12 to be perfectly aligned in every position. If the upper and lower bars should be arranged so that they pass each upon the comparatively frail pointer of the galvanometer when clamping the same. It should be apparent that the clamp bars could align themselves with an are about the center of the coil for only one adjusted position of the clamp bars if the clamp bars rotated about any axisother than substantially the axis of the coil.

The fact that the rocker 16 carries the rotatable ring 8i rather than being rotatable itself also gives rise to certain advantages. Thus, the cam and bell crank 5'! are prevented from exerting any rotative eiTort upon the clamp bars H and 12 such as would tend to move the clamp bars to a new position along the scale H8. It also keeps the axis about which the clamp bars tilt fixed with respect to the path of travel of the bushing 38 and the limited angle of motion of the pointer 36. Therefore, the axis about which the clamp bars rock can be given the most advantageous orientation with respect to the pointer 36 at every rotated position of the clamp bars. In the device shown and described in the present application, the axis about which the clamp bars rock or tilt is given that orientation which produces the greatest rise of the clamp bars in the region in which the pointer moves for a given angle of tilt. With this arrangement, the ring 3i which carries the clamp bars can be rotated through any angle, even 360, without diminishing the motion which the clamp bars execute in the region occupied by the pointer. This arrangement further permits the use of a simple mechanism for automatically disengaging the drive for adjusting the position of the clamp bars during the time that the clamp bars are raised to bring them into a clamping attitude with respect to the pointer 36.

The fact that the gear teeth on the ring 8| face upward permits them to disengage and swing clear of the teeth of the worm Hi When the clamping mechanism is tilted; and it permits these gear teeth to serve as a stop for the tilting and clamping mechanism when that mechanism drops to its lowermost position. By employing the worm l4, through its engagement with the teeth of the ring Bi, as the stop for the rocker 16 and the apparatus carried thereon, these teeth are brought firmly into engagement so as to eliminate any back lash or play between the teeth of the wormv Md and those of the ring 8!.

The apparatus of the present invention may be employed, for example, in a temperature regulating system, the temperature of the apparatus to be controlled may be measured by a resistance thermometer, thermocouple or other known electrical device, the galvanometer coil H of the present invention being employed therewith as the indicator or current measuring device. The pointer I22 may be adjusted to that position of the scale which corresponds to the temperature at which it is desired to maintain the controlled apparatus. The contacts of the clamp bars 1| and 12 may be arranged respectively to heat and cool that apparatus, or the cooling function for example may be omitted in which case only the contacts 74 of the clamp bar H will control a load. As long as the pointer 36 occupies the same scale position as the pointer I22, neither of the clamp bars I22 will operate its contacts. When the pointer 36 moves slightly to the left of the position indicated by the pointer 22, it will be caught by the clamp bar H and thereby will cause the heating apparatus to be set into operation each time that the clamp bars are raised by the motor 55. This will increase the temperature of the device being controlled so that the electrical temperature measuring apparatus connected to the coil I1 eventually will cause the pointer 36 to deflect towards the right. However, the pointer 36 will continue to cause the contacts which are associated with the arcuate clamp bar ll periodically to be operated until the temperature rises to such value that the pointer 36 moves to the position indicated by the pointer I22 or to the right thereof.

It will be apparent to those skilled in the art that the specific embodiment of the invention herein shown and described is illustrative only, and that the invention is capable of numerous modifications and variations. Therefore, the invention should not be limited except by thev scope of the appended claims.

We claim:

1. In combination in a device of the class described, a galvanometer having a pointer which is rotatable about an axis, a pair of clamp bars adapted to clamp said pointer and means for repeatedly moving at least one of said bars to bring said bars into a clamping attitude with respect to said pointer and to withdraw them therefrom, electric contact mechanism adapted to be operated by'mechanical force, at least one of said clamp bars being mechanically coupled to said contact mechanism so that the force with which said bars clamp said pointer serves to operate said switch.

2. In combination in a device of the class described, a galvanometer having a pointer which is rotatable about an axis, a pair of clamp bars adapted to clamp said pointer in rotated position, said clamp bars being arcuate and having the centers of their arcs substantially at said axis of said pointer and means for repeatedly moving at least one of said bars to bring said bars into a clamping attitude with respect to said pointer and to withdraw them therefrom, at least one of said bars being rotatable substantially about said axis of the galvanometer and extending less than 360 about said axis.

3. In combination in a device of the class described, a galvanometer having a pointer which is rotatable about an axis, said pointer consisting of a thin-wall metal tube,'a pair of clamp bars adapted to clamp said pointer, said clamp bars being arcuate and having the centers of their arcs substantially at said axis of the galvanometer, means for repeatedly moving at least one of said bars to bring said bars into a clamping attitude with respect to said pointer and to withdraw them therefrom, at least one of said bars being rotatable substantially about said axis of the galvanometer and extending less than 360 about said axis, and a bushing on said pointer for supporting the pressure exerted on said pointer by the clamping action of said clamp bars, said bushing being carried by said pointer on the portion thereof which encounters said clamp bars 4. In combination in a device of the class described, a galvanometer having a pointer which is rotatable about an axis, a graduated scale with respect to which said pointer indicates its own deflected position, a pair of clamp bars having clamping surfaces adapted to clamp said pointer, means for moving at least one of said bars to bring said clamp bars into a clamping attitude with respect to said pointer and to withdraw them there'- from, at least one of said bars being rotatable substantially about the axis of said pointer and having its clamping surface limited in the direction about said axis, a second pointer rotatable substantially about said axis with the rotatable clamp bar, said second pointer indicating on said graduated scale the position of the margin of the limited clamping portion of said rotatable clamp bar, said means including an electric contact mechanism adapted to be operated by mechanical force and so coupled to one of said clamp bars that the force with which said bars clamp said pointer serves to operate said switch.

5. In combination in a device of the class described, a galvanometer having a movable pointer, a pair of clamp bars having clamping surfaces adapted to clamp said pointer, means for repeatedly moving at least one of said bars to bring said clamp bars into a clamping attitude with respect to said pointer and to withdraw them therefrom, at least one of said clamp bars having its clamping surface so limited in extent as to cover less than the full path of motion of said pointer whereby said clamp bars are adapted to clamp said pointer only when said pointer occupies certain portions of its path of motion, electric contact mechanism adapted to be operated by mechanical force, at least one of said clamp bars being mechanically coupled to said contact mechanism so that the force with which said bars clamp said pointer serves to operate said switch.

6. In combination in a device of the class described, a galvanometer having a pointer which is rotatable about an axis through a limited angle, a pair of clamp bars for clamping said pointer, and means for moving at least one of said clamp bars so as to bring said clamp bars into a clamping attitude, said means comprising a support for said one clamp bar, said support being tiltable about a fixed axis which is substantially perpendicular to said axis of the galvanometer and which is substantially perpendicular to the median position of said pointer in said limited angle of rotation.

7. In combination in a device of the class described, a galvanometer having a coil carried on taut suspensions and having a pointer carried on said coil, said coil and pointer being rotatable through a limited angle, said pointer extending from said coil and having a clamp engaging portion removed from the axis of the taut wire suspensions in a radial direction and removed in a direction along said axis of the taut wire suspensions from the center of said coil, a pair of clamp bars for clamping said pointer, one of said clamp bars being movable about a tilting axis to bring said clamp bars into a clamping attitude, said tilting axis being substantially perpendicular to said axis of the taut wire suspensions and substantially perpendicular to a line radiating from the axis of the taut wire suspensions and intersecting the median position in the range of positions of the clamp engaging portion of said pointer, said range of positions of said clamp engaging portion being determined by said limited angle of rotation of said pointer, said tilting axis being located with reference to the direction of said axis of the taut suspension wires between said clamp engaging portion of said pointer and the center of said coil, said tilting axis being located with respect to the direction of said line radiating from the axis of the taut wire suspensions and intersecting said median position of said clamp engaging portion of said pointer, to that side of said clamp engaging portion of the pointer on which lies said axis of the taut wire suspensions.

8. In combination in a device of the class described, a galvanometer having a pointer which is rotatable about an axis through a limited angle, a pair of clamp bars adapted to clamp said pointer, at least one of said clamp bars being movable about a fixed tilting axis to bring said clamp bars into a clamping attitude, said fixed tilting axis being substantially perpendicular to the axis of rotation of the pointer and substantially perpendicular to the median position of said pointer in the limited angle of rotation thereof, at least one of said clamp bars being rotatable approximately about the axis of rotation of said pointer and extending about said axis less than 360.

9. In combination in a device of the class described, a galvanometer comprising a substantially closed housing, a coil therein and a pointer carried by said coil, said coil and pointer being rotatable about a coil axis through a limited angle, a pair of clamp bars adapted to clamp said pointer, means for moving at least one of said clamp bars so as to bring said clamp bars into a clamping attitude with respect to said. pointer, said means comprising a supporting structure for said one clamp bar, said supporting structure comprising a rocker supported on said housing and tiltable thereon about an: axis which is substantially perpendicular to the coil axis and substantially perpendicular to a median position of said pointer with respect to said limited angle, said supporting structure comprising also am'ember rotatable on said rocker about an axis. which is substantially coincident with said coil axis for one tilted position of said" rocker, said one clamp bar extending about said axis less than 360.

10. In combination in. a device of the class described, a galvanometer having a pointer which is movable along a path of travel thereof, a pair of clamp bars adapted to clamp said: pointer, first means for moving at least one of said clamp bars to bring said clamp bars into a clamping attitude with respect to said pointer and. to withdraw them therefrom, at least one of said clamp bars being movable along said path of travel of the pointer and being adapted to extend less than the full length of said path of travel in at least one position of said clamp bar along said path of travel, and second meansfor driving said last axis through a limited angle,. a pointer carried on said coil and rotatable therewith, said pointer extending out of said housing, a pair of clamp bars adapted to clamp said pointer, means for supporting one. of said clamp: bars, said means comprising a ring shapedrocker encircling said housing and supported thereon, said rocker being tiltable on said housing about a: rocker axis which is fixed with respect to said. housing, said means comprising. also a ring shaped rotatable member encircling said housing. carried.- on said rocker and rotatableon' said rocker about" a third:

axis which is fixed with respect to said: rocker, said one clamp bar being carried by said rotatable member and being rotatable. therewith, said one clamp bar extending less than360 about said coil axis and about said: third. axis andbeing adapted to engage said pointer at a point oiT said coil axis, off said. rocker axis and oil said third axis, whereby ('1'). said: one clamp bar is adapted to tilt. with said rocker into and out of a. clamping attitude with respect to said pointer;

(2) said clamp bar when in said clamping attitude is adapted to engage and clamp said pointer or to avoid clamping the same in accordance with the rotated position of said pointer relative to the rotated position of said one clamp bar; and (3) said clamp bar is adapted to rotate to change its rotated position, so as to change the respective rotated positions at which said pointer is adapted toescape and engage said clamp bar.

12. In combination in a device of the class described, a galvanometer comprising a substantially closed housing, a coil therein, and a pointer carried by said coil, said pointer and coil being rotatable together about a coil axis through a limited angle, a pair of clamp bars adapted to clamp said pointer, means for moving at least one of said clamp bars so as to bring said clamp bars into a clamping attitude with respect to said pointer and to withdraw them therefrom, said means comprising a supporting structure forsaidone clamp bar, said supporting structure comprising a rocker supported on said housing and tiltable thereon about a rocker axis, said rocker axis being fixed with respect to said housing, said supporting structure comprising also a member carried on said rocker and rotatable about a third axis, said third axis being fixed with respect to said rocker and lying approximately in the direction and position of said coil axis of the galvanometer, said one clamp bar being rotatable with said rotatable member and extending about said coil and third axes less than 360", a driving member for said rotatable member adapted to make driving engagement with said rotatable member" at a position off said third axis about which said rotatable member rotates on said rocker and off said rocker axis about which said rocker tilts, said rocker being adapted to tilt about said rocker axis to accomplish the following in a single motion in one direction of rotation about said rocker axis: (1) move said one clamp bar to bring said clamp bars into a clamping attitude with respect to said pointer; and (2) withdraw said rotatable member from driving engagement with said driving member.

13. In combination in a device ofthe class described, a galvanometer comprising a substantially closed housing, a coil therein and apointer carried onsaid coil, said coil and pointer being rotatable together about a coil axis through a limited angle, the median position of said pointer in said angle being forward of said housing, apair of clamp bars lying above and below the path of said pointer for clamping said pointer, means for moving the lower one of saidclamp bars so as to bring said clamp bars into a clampingattitude with respect to said pointer, saidmeans comprising a supporting structure for said lower clamp bar, said supporting structure com prising a rocker encircling said housing and having a circular seat encircling said housing, said rocker being supported on said housing and tiltable thereon about a rocker axis which is fixed with respect to said housing, said rocker axis ly-' ing substantially perpendicular to said coil axis and substantially perpendicular to said median position of said pointer in said limited angle, said supporting structure comprising also a rotatable member encircling said housing, said rotatable member being carried on said rocker and beingv rotatable on said seat about a third axis which is fixed with respect to said rocker and which is substantially coincident with said coil axis for one tilted position of said rocker, said lower clamp bar extending about said coil axis and about said third axis less than-360, said rotatable member having teeth arranged in a circular pattern thereon about said third axis, a worm engaging said teeth at the rear of said circular pattern, said worm being rotatable about an axis which is fixed with respect to said housing for rotating said rotatable member on said rocker, said axis of said worm lying approximately parallel to said rocker axis, said rocker axis lying forward of said axis of said worm and aft of said lower clamp bar, said teeth of said rotatable member being adapted to disengage said worm by dropping away therefrom, said rotatable member being adapted to tilt with said rocker about said rocker axis to accomplish the following in a single motion in one direction of rotation about said rocker axis: (1) raise said lower clamp bar into a clamping attitude with respect to said pointer; and (2) drop said teeth of said rotatable member out of engagement with said worm.

14. In combination in a device of the class described, a galvanometer comprising a substantially closed housing, a coil therein, and a pointer carried by said coil, said pointer and coil being rotatable together about a coil axis through a limited angle, a pair of clamp bars for clamping said pointer, means for moving at least one of said clamp bars so as to bring said clamp bars into a clamping attitude with respect to said pointer and to withdraw them therefrom, said means comprising a supporting structine for said one clamp bar, said supporting structure comprising a rocker supported on said housing,

and tiltable thereon about a rocker axis, said rocker axis being fixed with respect to said housing, said supporting structure comprising also a member carried on said rocker and rotatable about a third axis, said third axis being fixed with respect to said rocker and lying approximately in the direction and position of said coil axis, said one clamp bar being rotatable with said rtatable member and extending about said coil and third axes less than 360, a driving member for said rotatable member adapted to make driving engagement with said rotatable member at a position off said third axis about which said rotatable member rotates on said rocker and off said rocker axis about which said rocker tilts, said rocker being adapted to tilt about said rocker axis to accomplish the following in a single motion in one direction of rotation about said rocker axis: (1) move said one clamp bar to bring said clamp bars into a clamping attitude with respect to said pointer; and (2) withdraw said rotatable member from driving engagement with said driving member, a graduated scale cooperating with said pointer for indicating on said scale the rotated position of said pointer about said coil axis, a second pointer rotatable with said rotatable member for indicating on said scale the rotated position of said one clamp bar about said third axis.

15. In combination in a device of the class described, a galvanometer comprising a substantially closed housing, a coil therein and a pointer carried on said coil, said coil and pointer being rotatable together about a coil axis through a limited angle, the median position of said pointer in said angle being forward of said housing, a pair of clamp bars lying above and below the path of said pointer for clamping said pointer, means for moving the lower one of said clamp bars so as to bring said clamp bars into a clamping attitude with respect to said pointer, said means comprising a supporting structure for said lower clamp bar, said supporting structure comprising a rocker encircling said housing and having a circular seat encircling said housing, said rocker being supported on said housing and tiltable thereon about a rocker axis which is fixed with respect to said housing, said rocker axis lying substantially perpendicular to said coil axis and substantially perpendicular to said median position of said pointer in said limited angle, said supporting structure comprising also a rotatable member encircling said housing, said rotatable member being carried on said rocker and being rotatable on said seat about a third axis which is fixed with respect to said rocker and which is substantially coincident with said coil axis for one tilted position of said rocker, said lower clamp extending about said coil axis and about said third axis less than 360, said rotatable member having teeth arranged in a circular pattern thereon about said third axis, a worm engaging said teeth at the rear of said circular pattern, said worm being rotatable about an axis which is fixed with respect to said housing for rotating said rotatable member on said rocker, said axis of said Worm lying approximately parallel to said rocker axis, said rocker axis lying forward of said axis of said worm and aft of said lower clamp bar, said teeth of said rotatable member being adapted to disengage said worm by dropping away therefrom, said rotatable member being adapted to tilt with said rocker about said rocker axis to accomplish the following in a single motion in one direction of rotation about said rocker axis: (1) raise said lower clamp bar into a clamping attitude with respect to said pointer; and (2) drop said teeth of said rotatable member out of engagement with said worm, a graduated scale cooperating with said pointer for indicating on said scale the rotated position of said pointer about said coil axis, a second pointer rotatable with said rotatable member for indicating on said scale the rotated position of said one clamp bar about said third axis, said lower clamp bar being hinged on said rotatable member about an axis which is approximately perpendicular to said third axis, and contacts carried by said rotatable member and adapted to be operated by said lower clamp bar when said clamp bars engage and clamp said pointer.

16. In a device of the class described, a frame having a cylindrical portion, a galvanometer housed in said cylindrical portion of said frame, a rocker carried by said cylindrical portion, a ring positioned on said rocker and carried thereby, said ring encircling said cylindrical portion, a pair of clamp bars pivotally supported on said ring, a stationary clamp bar carried on said frame and positioned near each of said pivoted clamp bars, means carried on said frame for imparting a rocking movement to said rocker and for thereby rocking said pivoted clamp bars towards and away from said stationary clamp bar, a pointer actuated by said galvanometer and adapted to swing between said stationary clamp bar and said pivoted clamp bars, electrical contacts carried by said ring and adapted to be operated by said pivoted clamp bars, said ring, contact and pivoted clamp bars being rotatable together on said rocker, and a housing enclosing the foregoing apparatus.

17. In combination in a device of the class described, a galvanometer having a pointer which is rotatable about an axis, a pair of clamp bars adapted to clamp said pointer and means for moving one of said bars so as to bring said bars into a clamping attitude with respect to said pointer, said means including a power actuator and a driving connection between said power actuator and said one bar, and electric contact mechanism included in said driving connection adapted to be operated by the pressure with which said bars clamp said pointer.

18. The combination of the immediately preceding claim wherein said means includes a tiltable member carrying said contact mechanism, wherein said contact mechanism includes a movable part for urging said one clamp bar into its clamping attitude, and wherein said power actuator tilts said tiltable member to move said contact mechanism against said bar, whereby when the pointer obstructs the motion of said bar, the power actuator operates said switch mechanism.

19. In combination in a device of the class described, a galvanometer having a pointer rotatable about an axis, a pair of clamp bars adapted to clamp said pointer, means for moving one of said bars toward said pointer to bring said bars into a clamping attitude and electric contacts operated by said means when said bars clamp said pointer, said means including a tiltable member and a power actuator for tilting it, said contacts comprising a pair of cantilever contact blades supported on said tiltable member, one of said blades being flexible and bearing against said one contact bar to urge it toward clamping position as said tiltable member tilts so that when the pointer obstructs the motion of said bar said one blade must flex as said tiltable member tilts, whereby to operate said contacts.

20. In combination in a device of the class described, a galvanometer having a pointer which is rotatable about an axis, said pointer consisting of a thin-wall tube, a pair of clamp bars adapted to clamp said pointer, means for moving at least one of said bars to bring said} bars into a clamping attitude with respect to said pointer, and a bushing on said pointer for supporting the pressure exerted on said pointer by the clamping action of said clamp bars, said bushing being carried by said pointer on the portion thereof which encounters said clamp bars.

21. In combination in a device of the class described, a galvanometer having a pointer which is movable along a path of travel thereof, a pair of clamp bars adapted to clamp said pointer, means for moving at least one of said clamp bars to bring said clamp bars into a clamping attitude with respect to said pointer and to withdraw them therefrom, at least one of said clamp bars being movable along said path of travel of the pointer and being adapted to extend less than the full length of said path of travel in at least one position of said clamp bar along said path of travel, and adjusting means for driving said last mentioned one clamp bar along said path of travel, said last means being operable only when said clamp bars are not in a clamping attitude with respect to said pointer, said adjusting means being incapable of operating said clamp bars into or out of a clamping attitude with respect to said pointer.

22. In combination in a device of the class described, a galvanometer having a pointer rotatable about an axis, means for detecting the position of said pointer, said means including a clamp bar adapted to be moved toward said pointer to bring it into a clamping attitude with respect thereto, a tiltable member having a projection thereon for supporting a contact structure, a sheet of insulating material folded over said projection to cover the extended end and two opposed faces of said projection, the ends of said sheet extending out away from said opposed faces of said projection, and contact blades mounted cantilever fashion on said projection on the outside of said sheet of insulating material, said sheet being wider than either said projection or said contact blades, said tiltable member being adapted to rock said contacts against said clamp bar to urge said bar toward said pointer.

ARCHIE J. McMASTER.

WALTER VAN GUILDER. 

